Well, this is an annoying requirement, particularly for those of us who use one-off e-mails per service.
Since I used different e-mail addresses to register for PyCon US 2022 and 2023, I can't just point the PyCon US 2023 website at my existing Sharemyhealth account.
Please don't use e-mail as a primary key or a username or whatever it is that is causing this requirement (or any of the other similar problems like "You can't change your e-mail")